Sqlite 如何在flatter中使用SQFlite进行数据库查询
如何使用SQFlite插件从Flatter中的SQLite数据库查询数据 我最近一直在学习这一点,因此我在下面添加我的答案,作为帮助我学习的一种方法,也作为将来其他人的快速参考。添加依赖项 打开Sqlite 如何在flatter中使用SQFlite进行数据库查询,sqlite,dart,flutter,sqflite,Sqlite,Dart,Flutter,Sqflite,如何使用SQFlite插件从Flatter中的SQLite数据库查询数据 我最近一直在学习这一点,因此我在下面添加我的答案,作为帮助我学习的一种方法,也作为将来其他人的快速参考。添加依赖项 打开pubspec.yaml并在依赖项部分添加以下行: sqflite: ^1.0.0 path_provider: ^0.4.1 当然,sqflite是插件,path\u提供程序将帮助我们获得Android和iPhone上的用户目录。您可以在此处查看最新版本号:和 创建一个数据库帮助器类 我在单例类中保留
pubspec.yaml
并在依赖项部分添加以下行:
sqflite: ^1.0.0
path_provider: ^0.4.1
当然,sqflite
是插件,path\u提供程序
将帮助我们获得Android和iPhone上的用户目录。您可以在此处查看最新版本号:和
创建一个数据库帮助器类
我在单例类中保留对数据库的全局引用。这将防止并发问题和数据泄漏。您还可以在此处添加帮助器方法(如查询)以访问数据库
创建一个名为database_helper.dart的新文件,并用以下代码粘贴:
import 'dart:io' show Directory;
import 'package:path/path.dart' show join;
import 'package:sqflite/sqflite.dart';
import 'package:path_provider/path_provider.dart' show getApplicationDocumentsDirectory;
class DatabaseHelper {
static final _databaseName = "MyDatabase.db";
static final _databaseVersion = 1;
static final table = 'my_table';
static final columnId = '_id';
static final columnName = 'name';
static final columnAge = 'age';
// make this a singleton class
DatabaseHelper._privateConstructor();
static final DatabaseHelper instance = DatabaseHelper._privateConstructor();
// only have a single app-wide reference to the database
static Database _database;
Future<Database> get database async {
if (_database != null) return _database;
// lazily instantiate the db the first time it is accessed
_database = await _initDatabase();
return _database;
}
// this opens the database (and creates it if it doesn't exist)
_initDatabase() async {
Directory documentsDirectory = await getApplicationDocumentsDirectory();
String path = join(documentsDirectory.path, _databaseName);
return await openDatabase(path,
version: _databaseVersion,
onCreate: _onCreate);
}
// SQL code to create the database table
Future _onCreate(Database db, int version) async {
await db.execute('''
CREATE TABLE $table (
$columnId INTEGER PRIMARY KEY,
$columnName TEXT NOT NULL,
$columnAge INTEGER NOT NULL
)
''');
// prepopulate a few rows (consider using a transaction)
await db.rawInsert('INSERT INTO $table ($columnName, $columnAge) VALUES("Bob", 23)');
await db.rawInsert('INSERT INTO $table ($columnName, $columnAge) VALUES("Mary", 32)');
await db.rawInsert('INSERT INTO $table ($columnName, $columnAge) VALUES("Susan", 12)');
}
}
一排
我们可以为where
参数传入一个参数,以选择符合条件的特定行。在本例中,我们将查询ID为1
的行
_query() async {
// get a reference to the database
Database db = await DatabaseHelper.instance.database;
// get single row
List<String> columnsToSelect = [
DatabaseHelper.columnId,
DatabaseHelper.columnName,
DatabaseHelper.columnAge,
];
String whereString = '${DatabaseHelper.columnId} = ?';
int rowId = 1;
List<dynamic> whereArguments = [rowId];
List<Map> result = await db.query(
DatabaseHelper.table,
columns: columnsToSelect,
where: whereString,
whereArgs: whereArguments);
// print the results
result.forEach((row) => print(row));
// {_id: 1, name: Bob, age: 23}
}
确保使用?
字符串替换使用数据绑定。这将防止SQL注入攻击
笔记
- 如果您在另一个文件(如main.dart)中,则必须导入
类和DatabaseHelper
sqflite
- SQFlite插件使用
将列名映射到每行中的数据Map
main.dart
的布局代码:
import 'package:flutter/material.dart';
// I called my project 'flutter_database_operations'. You can update for yours.
import 'package:flutter_database_operations/database_helper.dart';
import 'package:sqflite/sqflite.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'SQFlite Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('sqflite'),
),
body: RaisedButton(
child: Text('query', style: TextStyle(fontSize: 20),),
onPressed: () {_query();},
),
);
}
_query() async {
// get a reference to the database
Database db = await DatabaseHelper.instance.database;
// get all rows
List<Map> result = await db.query(DatabaseHelper.table);
// get single row
//List<Map> result = await db.query(DatabaseHelper.table,
// columns: [DatabaseHelper.columnId, DatabaseHelper.columnName, DatabaseHelper.columnAge],
// where: '${DatabaseHelper.columnId} = ?',
// whereArgs: [1]);
// raw query
//List<Map> result = await db.rawQuery('SELECT * FROM my_table WHERE name=?', ['Mary']);
// get each row in the result list and print it
result.forEach((row) => print(row));
}
}
导入“包装:颤振/材料.省道”;
//我把我的项目称为“颤振数据库操作”。您可以为自己的更新。
导入“包:flatter_database_operations/database_helper.dart”;
导入“包:sqflite/sqflite.dart”;
void main()=>runApp(MyApp());
类MyApp扩展了无状态小部件{
@凌驾
小部件构建(构建上下文){
返回材料PP(
标题:“SQFlite演示”,
主题:主题数据(
主样本:颜色。蓝色,
),
主页:MyHomePage(),
);
}
}
类MyHomePage扩展了无状态小部件{
@凌驾
小部件构建(构建上下文){
返回脚手架(
appBar:appBar(
标题:文本(“sqflite”),
),
主体:升起按钮(
子项:文本('query',样式:TextStyle(fontSize:20),),
onPressed:(){u query();},
),
);
}
_查询()异步{
//获取对数据库的引用
Database db=await DatabaseHelper.instance.Database;
//获取所有行
List result=await db.query(DatabaseHelper.table);
//获得单行
//List result=await db.query(DatabaseHelper.table,
//columns:[DatabaseHelper.columnId,DatabaseHelper.columnName,DatabaseHelper.columnAge],
//其中:“${DatabaseHelper.columnId}=?”,
//其中:[1]);
//原始查询
//List result=wait db.rawQuery('SELECT*FROM my_table,其中name=?',['Mary']);
//获取结果列表中的每一行并打印它
result.forEach((行)=>打印(行));
}
}
进行中
- 这篇文章是对我之前文章的发展:。有关其他SQL操作和建议,请参阅该帖子
_query() async {
// get a reference to the database
Database db = await DatabaseHelper.instance.database;
// raw query
List<Map> result = await db.rawQuery('SELECT * FROM my_table WHERE name=?', ['Mary']);
// print the results
result.forEach((row) => print(row));
// {_id: 2, name: Mary, age: 32}
}
import 'package:flutter/material.dart';
// I called my project 'flutter_database_operations'. You can update for yours.
import 'package:flutter_database_operations/database_helper.dart';
import 'package:sqflite/sqflite.dart';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: 'SQFlite Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(),
);
}
}
class MyHomePage extends StatelessWidget {
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('sqflite'),
),
body: RaisedButton(
child: Text('query', style: TextStyle(fontSize: 20),),
onPressed: () {_query();},
),
);
}
_query() async {
// get a reference to the database
Database db = await DatabaseHelper.instance.database;
// get all rows
List<Map> result = await db.query(DatabaseHelper.table);
// get single row
//List<Map> result = await db.query(DatabaseHelper.table,
// columns: [DatabaseHelper.columnId, DatabaseHelper.columnName, DatabaseHelper.columnAge],
// where: '${DatabaseHelper.columnId} = ?',
// whereArgs: [1]);
// raw query
//List<Map> result = await db.rawQuery('SELECT * FROM my_table WHERE name=?', ['Mary']);
// get each row in the result list and print it
result.forEach((row) => print(row));
}
}